Some power conversion devices are configured from a 12-phase rectifier transformer in order to prevent harmonics from leaking to the AC system. In 12-phase rectifier transformers, there are configurations where the primary side is configured as a Y-connection and the secondary side is configured as a Δ-connection and a Y-connection, and there are configurations where the primary side is configured as a Δ-connection and the secondary side is configured as a Δ-connection and a Y-connection. A 12-phase rectifier transformer performs 12-phase rectification by generating a three-phase alternating current having a phase difference of 30 degrees on the secondary side so that full-wave rectification can be performed (see Patent Literature 1).